1. Technical Field
The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus to scan a target surface using a plurality of light beams, and an image forming apparatus employing the optical scanning apparatus.
2. Description of the Background Art
Image forming apparatuses using electrophotography use a laser beam for optical scanning. Such image forming apparatuses use an optical scanning apparatus typically including a polygon scanner (e.g., polygon mirror), by which a surface of a photoconductive drum is scanned by the laser beam to form a latent image on the surface of the photoconductive drum. Such electrophotographic image forming apparatuses enhance image quality by forming images with high image density, and enhance image forming productivity by forming images with high speed. Such high image density and high speed imaging can be achieved by scanning the drum surface, that is, by irradiating the drum surface with a plurality of light beams simultaneously, a method that can be called multi-beam scanning.
For example, JP-3549666-B (JP-H09-274152-A) discloses a multi-beam scanning system that reduces differences in curvature of scanning lines to a given level so that images can be produced correctly.
However, as for such multi-beam scanning system, if the numbers of light beams become three or more and ambient temperature changes, the beam pitch on the target surface in the sub-scanning direction starts to fluctuate greatly.